1. Field of the Invention
The invention relates to an electrodeposition-coating monitoring system and method, and a method of manufacturing an electrodeposition-coated article, in which an electrodeposition coating apparatus for performing electrodeposition coating by conveying an object to be coated while the object is immersed in a liquid electrodeposition paint. More specifically, the invention relates to an electrodeposition-coating monitoring system and method, in which an apparatus is monitored in which objects to be coated are continuously conveyed and electrodeposition coating on a plurality of objects to be coated is performed in parallel, and to a method of manufacturing electrodeposition-coated articles in which the electrodeposition-coated articles are manufactured while monitoring is performed.
2. Description of the Related Art
In a process of undercoating a body of a car, electrodeposition coating has been widely performed in which the body is immersed in a liquid electrodeposition paint in an electrodeposition bath. In the electrodeposition bath, many electrodes are disposed on the side surfaces and the bottom surface of the electrodeposition bath. When an undercoating process is performed, objects to be coated are conveyed in the electrodeposition paint while voltage is applied to these electrodes. In such an electrodeposition coating apparatus, thought is given to the shape and arrangement of the electrodes so as to form a coat on the surface of the coated objects evenly as much as possible (see Japanese Patent Application Publication No. 8-199398 (JP-A-8-199398)).
Japanese Patent Application Publication No. 2006-97119 (JP-A-2006-97119) describes a method of measuring the amount of coating and the thickness of the coat on each object to be coated in an apparatus in which a plurality of objects to be coated are simultaneously immersed in an electrodeposition paint by continuously conveying a plurality of objects to be coated along the electrodeposition bath. According to the technology described in this document, the variation with time of the values of the electric currents flowing through a plurality of electrodes is measured, and the component corresponding to the object to be coated concerned is extracted from the variation with time and integrated. This document says that, in this way, it is possible to obtain the number of coulombs that flow through the object to be coated concerned, and based on the number of coulombs, it is possible to calculate the amount of coating.
However, in the system described in the above JP-A-2006-97119, the data concerning the variation with time of the electric current value is used to differentiate a plurality of objects to be coated from each other that are simultaneously conveyed. Although it is possible to determine the total amount of coating for each object to be coated during a coating process with the use of this system, the system is not designed to determine the electric current value when the object to be coated is at the position at which the object faces an electrode. Thus, there has been a problem that even when a failure occurs in an electrode, for example, it is difficult to detect the occurrence of the failure when the variation in the amount of coating is compensated for by another electrode.
In addition, when it is intended to measure the total amount of coating, the result can be obtained only after the object to be coated is taken out. Thus, depending on the portion in which the failure occurs, there has been a fear that defects can occur in the objects to be coated that are put into the bath after the occurrence of the failure.